Honing brake master cylinder

Hi all,

Sorry for taking the forum by storm - I've got a lot of questions that Googling has not turned up!

I took the master cylinder off and apart a while ago, and since then it seems as though the residual brake fluid has eaten into the bore and some other parts, like the little metal plate inside the fluid reservoir (is this possible?). Whatever the reason, the bore's a little pitted, so I'd like to hone the master cylinder to get it smooth again. I'm looking at ball hones online -- what grit should I be using?

Thanks!!

If you manage to hone enough out of the bore to remove pits id be willing to bet the bore would become too big for the seals to work.

Master cylinders cores in this condition need to be replaced.

They are not a good candidate for rebuild or to enlarge the bores.

Can it be done? a light hone yes.

Aggressively honing the bore to remove pitting and enlarging the O.D. you are compromising the effectiveness of the master cylinder.

Is it a single front brake, dual front brake or a rear master?

I would purchase a good used core off Flebay and rebuild it.

I know a-little about these rascals.

I have always been curious on whether a motorcycle M/C can be honed. Been a long time but I use to do it on automobile M/C's. Last time I did it was over 30 years ago. Maybe for cars there must be some aftermarket kits that are larger than the OEM kits? For bike I just figured the bore is too small and never seen honing stones that small anyways. Figured it's just not done. Anybody out there does this on car M/C's?

The typical 3 stone hone would not be used for this operation.

They do make bore size spiral brushes that have a cutting aggregate attached or impregnated to the brush bristles. They are stiff and really can take a lot of material off,

They are used the same, as you would spin then white moving them in and out.

Very much like if not considered a BALL hone.

Thanks, for the post, glad to hear the option is there. From what I remember from those days (had auto shop class in high school), the theory behind honing is to apply a cross hatch pattern to the bore. In this case it will actually decrease the diameter by ever so slightly as opposed to boring. In other words, by scribing the cylinder with the stones (or ball hone as well I suppose) in diamond (cross hatch) pattern, you are displacing some of the material (not removing) which will cause high spots (surface) throughout the cylinder. So I would think the idea is not to remove the pits, but create the higher surface area throughout the cylinder to compensate for the wear which occurred over time. So, I take back my previous post about maybe there was some kind over size M/C kits. The honing would make it fit better with the OEM type size kit. The lesson was specific to the engine cylinders, but is pertinent to all cylinder / pistons. Like I said, it has been a long time and we learned this at very early part of the morning, started at 7:00 AM I think. So my facts may be way out there. So please don't think I am speaking facts. Some with actual knowledge can chime in.

No eBay APP ID and/or Cert ID defined in Kunena configurationHave used very fine wet/dry sand paper to "dress" the bore surface, which smooths over any peaks, but doesn't affect minor pitting depressions, and the rubber cups worked just fine with no fluid leakage.

Brake cylinder two-stone hone is believed available that would be small enough to run inside a 14mm m/c bore.







Good Fortune!

Bad idea to try to hone the cylinder. Honing does not create raised crosshatched edges, it takes off material. By the time the corrosion marks are gone the bore will be out of round and way oversize. Chuck the master in the trash and look for a new (used) one, only be prepared to search before finding a clean one.

On my 750/4 the master has 49mm bolt hole spacing. There are aftermarket masters available with that same spacing that an inventive person could adapt, but be careful, most of the aftermarket units use 45mm spacing.

If sourcing an aftermarket unit, it is important that the volume moved by a piston stroke is close to the original unit. Too much volume moved = touchy brakes, too little volume moved = no brakes.

Kawasaki used a 14mm piston for most rear masters. The most common aftermarket size is 1/2", which is 12.7mm. This switch will result in more lever travel for the same braking force, but the force needed to press the pedal will go down.

OK, thanks for the input. I won't try honing the master cylinder, then. However, a better first question probably would have been: do you guys think this master cylinder is usable/salvageable? I tried to get some shots of the inside last night:



[sorry for the imgur link, uploading images directly to the site keeps giving me a 'fatal error']

I wouldnt spend anytime on that one, time for a replacement.